1. Field of the Invention
This invention relates generally to the field of aqueous metal siliconate solutions and amorphous materials derived therefrom, and to uses thereof, including both the treatment of various substrates and the modification of water-reducible protective coating systems.
2. Description of the Prior Art
Certain metals and metal compounds have long been known for their antimicrobial nature. Copper and zinc oxide are two such materials. For example, zinc oxide has been used as a primary ingredient in ointments and salves. Zinc oxide has been found to be environmentally and toxicologically unobjectionable, and it is inexpensive.
Attempts have been made to dissolve useful amounts of compounds of metals such as copper and zinc in ammoniacal solutions; however, the readily available oxides of zinc and copper are relatively poorly soluble even in aqueous ammonia. The most successful such efforts have been by adding the metal oxides to aqueous ammonia containing acidic ammonium salts such as ammonium carbonate or ammonium thiocyanate (U.S. Pat. No. 3,945,834). In this way the metal oxide is converted to a water soluble salt of the acid wherein the metal cation is coordinated with several ammonia molecules. Although the solubility of zinc oxide or basic cupric carbonate in aqueous ammonia is greatly enhanced by the presence of such acidic salts, their use has the attendant disadvantage of introducing large amounts of leachable non-functional salts to treated objects. For instance, wood impregnated with such solutions would contain large quantities of leachable ammonium carbonate, ammonium thiocyanate, etc. Furthermore, the metal salts themselves may tend to be too easily leachable for optimum long term protection.
Such metal salts are sometimes too easily redissolved and removed from the treated material during rains or washing. The use of too readily leachable complexes containing metals, such as copper, known to be offensive in high concentrations to living things, is environmentally undesirable. Indeed, such complexes may be quite poisonous when they are too readily leached into the surrounding terrain during normal weathering.
Furthermore, such metal salts do not impart a hydrophobic nature to materials which have absorbed them. Since water repellency is a desirable characteristic which aids in the preservation of cellulosic fibers and masonry, materials which provide hydrophobicity in addition to antimicrobial properties are desirable.
Although alkali metal and alkaline earth metal organosiliconates are described in the patent literature (U.S. Pat. Nos. 2,507,200 and 2,438,055) and in the scientific literature [C. G. Ladenburg, Ann. 173, p. 148; Meads and Kipping, J. Chem. Soc. 105, p. 679; and Kather and Torkelson, Ind. and Eng. Chem. 46(2), p. 381 (1954)], none of these disclosures teaches the use of ammonia to stabilize siliconate salts of metals. These materials have the serious disadvantage of leaving water soluble alkali metal or alkaline earth metal salts in treated objects, the presence of which can adversely affect the hydrophobicity otherwise obtainable by the organosilicon resin deposit.
The preparation of various metalorganosiloxanes by the reaction of the sodium salts of organosilanetriols with metal chlorides in organic solvents is disclosed by A. A. Zhdanov, K. A. Andrianov and M. M. Levitskii in the U.S.S.R. publication Seriya Khunicheskaya, No. 2, pp. 395-399, February, 1976. The compounds, which are made by a relatively tedious and complicated procedure, so disclosed are of low molecular weight and are soluble in organic solvents.